Compositions and method for use in plugging a well

ABSTRACT

A composition for use in plugging a well includes a mud having a plurality of plugging members therein, wherein the plugging member has a density more than about eight times that of water. A method of providing the composition into the well is also provided.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates in general to oil and gas wellremediation. More particularly, the invention relates to compositionsand method for use in plugging a well.

2. Prior Art

In drilling a well, there is created a connection to the oil and/or gasreservoir and tubing is installed between the reservoir and the surface.The outer steel casing requires a gas tight seal between the reservoirand the surface wherein an annulus (the gap between the casing and therock/formation) is typically subjected a cementing (or grouting)operation. This treatment is normally referred to as Primary Cementing.The main aspects of primary cementing are to isolate flow betweendifferent reservoirs, to withstand the external and internal pressuresacting upon the well by offering structural reinforcement and to preventcorrosion of the steel casing by chemically aggressive reservoir fluids.

A poor cementing job can result in migration of reservoir fluids, evenleading to gas migration through micro-annuli in the well which not onlyreduces the cost-effectiveness of the well but may cause a “blow out”resulting in considerable damage. Although repair jobs (“secondarycementing”) are possible (in essence forcing more cement into the cracksand micro-annuli) they are costly and do not always lead to the desiredresults.

A “blowout” refers to the uncontrolled flow of well fluids from a welland “fluids” refer to both liquids and gases. Recently, offshoredrilling operations have resulted in a major blow out.

Production tubing string includes a conduit in the well structure whichcontains petroleum fluids under pressure which, under conditions of ablowout, are uncontrollably escaping from some point along the verticaldevelopment of the conduit.

In such blow outs, oil leaks into rock formations outside the well. Ifthe rock is porous, the oil would eventually bubble up from differentspots in the ocean floor. It's important to know how high up in the wellany breach or crack is. The higher it is, the worse the scenario becausethe closer it is to potentially porous rock and the ocean.

The well leak could be significantly worse than what's been measuredfrom the end of the pipe. If you only measure the flow coming out of theend of the well bore, you're missing what is spurting from the break inthe pipe. The clogging of the break is imperative in order to plug thewell and minimize the ecological disaster.

In a small crack or break, a relatively small volume of cement(typically in the order of 100 m) is used to place the plug, its qualityneeds to be sufficient as it will serve as a seal for a very long time.However, in underwater operations, it is difficult to provide opposingfluid flow and plugging material.

The customary abandonment operation is very costly, especially in anoff-shore environment, since it typically requires the use of a workoveror drilling rig. It would be very beneficial if methods were availablewhich could lead to abandonment of wells without the necessity to removethe production tubing.

One of the major drawbacks of using traditional cementing materials suchas Class G Cement (e.g. OPC: Ordinary Portland Cement) in plugging isthat such materials cannot achieve a gas tight seal. In the search foreffective cementing materials, attention has to be paid to the materialshould be gas-tight (i.e. withstand a predetermined bar per m), itshould have a controllable setting time so that a range of temperaturesand well depths (each requiring different conditions) can be coped with,it should be thermally stable up to a predetermined temperature as wellas being chemically stable against reservoir fluids for a very longperiod of time and its properties should be such that pumping throughexisting oil field equipment can be carried out without many problems.

A wide range of non-cement plugging agents have been attempted whichinclude resins, golf balls, tire bits, for example. However, suchmaterials have not met with great success. Compositions consistingessentially of a mixture of slurry of hydraulic cement (such as Portlandcement) and rubber latex have been used. The use of putty (“mastic”) hasbeen disclosed for producing joints separating zones in wells.

Still others provide a method for controlling well blow outs, especiallywhen those located in a body of water and the well cannot beconventionally controlled using drilling mud. The environmental hazards,as well as the hazards to personnel, of well blow outs have becomeincreasingly important, especially where those blow outs have takenplace in ecologically sensitive areas, such as the coast of the UnitedStates. None of the prior methods proves to be a universal application,and each poses some economic or technological drawback.

Some disclose methods and apparatus for producing deep boreholes inwhich the borehole is filled at least partially with a substance whichremains in the liquid state and has a density greater than the meandensity of the ground strata being drilled. Thus, any infiltrations fromthe formation into the borehole, as well as drilling debris, naturallymove upward to the free surface of the liquid substance filling theborehole.

One prior method employs a so called “hot tap” which is a connection ofa fluid-conducting conduit to a second conduit without the need fordecreasing the pressure of the contents of the second conduit andwithout any substantial pressure loss or loss of the contents of thesecond conduit through the point of connection with the first conduit.U.S. Pat. No. 3,647,000 employs a method for capping the uncontrolledflow of oil and gas from petroleum wells located in a body of water. Themethod involves the tapping of a window or access opening into the wellcasing or tubing through which the well fluids are flowing below thesurface of the well, crimping the casing or tubing above the point ofthe tap and injecting solid plugging bodies which lodge within theconstriction in the production tubing string and form a plug blockingthe flow. Heavy non-combustible mud is then pumped into the productiontubing through the tapped-in access line until the weight of theinjected mud overcomes the formation pressure, thus terminating wellflow. Neither the nature of the plugging bodies nor the nature of theheavy mud is specified.

U.S. Pat. No. 3,926,256 discloses a method for preventing blow outs inoffshore wells. There is an apparatus in which pins extend into thepassage through which oil or gas are flowing, the uncontrolled flowbeing stopped by the injection into the pin-containing region of asealer material such as balls of rubber or fiber, natural or synthetic,Fiberglas, aluminum, shredded Teflon, and the like, followed by a masticwhich acts as the sealing agent.

U.S. Pat. No. 4,133,383 discloses a method for terminating formationfluid blow outs by introducing into the formation a low viscosity fluidwhich has the property of becoming highly viscous under the influence ofheat.

It is also known to apply dry ice or liquid nitrogen to the exterior ofthe string through which the well is blowing out and thereby freeze theblowing fluids to form a plug in the string. In another development, thecasing string through which the Ixtox I well in the Gulf of Mexico wasblowing out during the summer of 1979 was treated with some success inan effort to cut down the flow by pumping in iron and lead balls.

A major problem with high pressure deep wells is that the mud andplugging components are not effective for various reasons. For example,the plugging components cannot descend to a depth necessary to performtheir job in the face of the up-flow. Another problem is that thematerial breaks down prior to reaching the break or desired zone.

The present invention overcomes the above problems. The presentinvention provides for repair and abandonment operations in the face ofhigh pressure deep wells.

SUMMARY OF INVENTION

It is an object to plug a well blow out.

It is another object to provide a composition for use in plugging awell.

Accordingly, the instant invention is directed to a composition andmethod for use in plugging a well. The invention provides a heavy metal,such as lead ball or other suitable geometric shape, which is covered bya highly resilient coating, such as steel, polymer, or ceramic, whichcan survive the sheer force as they fall against a fairly strong flowingstream so they can aggregate at the bottom of the well or pack into thebreak. Over time, a sufficient number of balls delivered would fill upover the perforations thereby plug the ability of the formationspressure to push production upward. Thus, this would stop the flow.

Such heavy metals and members can include those that can have theability to expand and adhere to surfaces they come into contact withthat can be used in conjunction with the balls either as a coating orembedded into them. Further, the plugging composition can be equippedwith ability to become more stable once they arrive at the break orbottom of the wellbore. Preferred geometric designs can include roundand or cone shaped as a method to reduce the drag or tendency of theflow to lift is a very important feature as well. In the instantinvention, a hopper with a valve can open to deliver the compositionwhich connected downstream of a pump to the pipe going into thewellbore. The composition drilling mud can be pumped and the drillingmud will carry these plugging members (e.g., balls) and keep themsuspended in the thick fluid. The composition is configured as amechanism to deliver these balls to the site with sufficient ability topermit the balls to descend downward. The size and shape and make-up ofthe balls and carrier mud fluid are factors which provide necessaryblocking or plugging effect.

With a direct line “unobstructed” open hole into a well, a string ofcoil tubing or small diameter conventional tubing can be injected intothe existing tubing or open wellbore in a sight line. Optionally, theuse of a blowout preventer can be employed to carry out delivery. Thesmall string tubing would be used to pump down the plugging members(balls or cones) into the well near the bottom. A method can be providedto deliver of the plugging members into a hopper that is connected tothe coil tubing just below the mud pump whereby these balls or comeswould be injected into the stream of mud being pumped down.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation partially broken away of an exemplary wellinstallation employed in wells located in water;

FIG. 2 is a partial elevation partially broken away illustrating aportion of the well structure of FIG. 1 and the implementation of oneembodiment the invention;

FIG. 3 illustrates a plugging element of one embodiment of theinvention;

FIG. 4 is a partial elevation partially broken away illustrating aportion of the well structure of FIG. 1 and the implementation ofanother embodiment the invention;

FIG. 5 illustrates a plugging element of another embodiment of theinvention; and

FIG. 6 is a schematic illustrating an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, the composition and method of presentinvention is generally designated by the numeral 10 and is for use withdeep high pressure wells located in water. It will be understoodhowever, that the present invention can be employed with wells locatedon land.

A typical well structure is designated by the numeral 4 is illustratedwithin a body of water indicated generally at W. The well structure 4extends above the top of the surface of the water W and normallyterminates at a well head (not shown) which includes regulating andcontrol equipment and fittings for conducting the well fluids to acollection point.

The structure 4 includes an external conductor pipe 30 which extendsfrom above the surface of the water W to a point somewhat below thesurface of the water bed indicated generally at S. Typical intermediatecasing string 32 and a producing casing string 34 are carriedconcentrically within the conductor pipe 30 and extend to differentsubterranean points within the well bore. Concrete 36 is illustratedwithin the annular space between the conductor pipe 30 and intermediatecasing string 32. A production tubing string 38 extends through thecenter of the well structure 4 and is normally the principle conductoremployed for conveying the petroleum fluids from the subterraneanformation to the wellhead. Under normal conditions, with a wellstructure such as illustrated in FIG. 1, petroleum fluids in theformation are conducted through the production tubing string 38. Theintermediate and production casing strings 32 and 34 normally containlittle or no pressure and effluent flow is limited to the productiontubing string 38.

Pressure estimates for deep offshore wells range from 3500 psi to9500+ps or from 20 MPa to 65 MPa. It is not uncommon for the well borediameter to be large for example a foot in diameter. A blowout requiresimmediate remediation.

Plugging the hole can include the use of coiled tubing 13 wherein coiledtubing is run into the hole and pumping the composition 12 with pluggingmembers 16 enable killing fluid flow. Coiled tubing can be aconventional continuous length of low-alloy carbon-steel tubing that canbe spooled on a reel and deployed into a wellbore B for deliveringcomposition 12. One method is to inject the tubing 13 to near theperforations P. However, if this cannot be achieved due to debris in thewellbore B, the tubing 13 can be injected to a depth where it ispossible and by creating a large flow of mud 15 with plugging members16, the well flow will be reduced allowing the plugging members 16 tofall from such point to the bottom of the well.

Optionally, a blowout preventer 14 which includes a manifoldcommunicably connected to receive the composition 12 which includesplugging members 16 of the instant invention can be provided. Thecomposition 12 includes noncombustible high-density well controlmaterial or “mud” 15 and the plugging members 16, As seen in section inFIGS. 3 and 5, the plugging members 16 can include a core 18, such asheavy metal with one or more coating 19 and 20 which can be a frictionreduced and or durable coating, such as a polymer, steel, or ceramiccoating.

Sample Density of materials are as follows:

metal g/cm{circumflex over ( )}3 lb/in{circumflex over ( )}3lb/ft{circumflex over ( )}3 lb/gal water 1.00 0.036 62 8.35 aluminum2.70 0.098 169 22.53 zinc 7.13 0.258 445 59.50 iron 7.87 0.284 491 65.68copper 8.96 0.324 559 74.78 silver 10.49 0.379 655 87.54 lead 11.360.410 709 94.80 mercury 13.55 0.490 846 113.08 gold 19.32 0.698 1206161.23

Some material is cost prohibitive in addition to being malleable whileothers are less costly, yet malleable and toxic such as lead andmercury. In order to use these materials, the material is to be coatedwith a sufficient coating to permit use under the rough forces withinthe well bore, i.e., be pushed down by the drilling fluids using pump17, e.g., 20,000 hp.

To this end, a sufficiently sized plugging member 16 can be formed oflead for example and then coated with a suitable coating. One coatingfor use with the invention can include Molybdenum Disulfide (MoS2)combined with one of nylon (with the trade name Nylatron), Teflon, andVespel. Another self-lubricating composite coating for high-temperatureapplication includes molybdenum disulfide and titanium nitride formed bychemical vapor deposition. Other silicon based ceramics includingsilicon nitride and silicon carbide can be used their high temperaturestrength and relative corrosion resistance.

The concept is to provide a sufficient resistant force with the blowoutpreventer to permit the coated pellets to drop to the well blockingpoint. The coating 19 and/or 20 permits the normally mechanically weak,but heavy material to survive a mile long journey under very highpressure in 1200 gpm within a rigid pipe. The coating 19 or 20 can be adrag reducing material such as a hydrophobic coating, such as WearlonSuper F-6M™ available from Industrial Coating Systems in China. It isalso contemplated that one of the coating 19 or 20 can include a welltreating agent. Optionally the coating 19 or 20 can include adissolvable material, such as a soluble polymer, which can house theheavy substance or adhesive substance such that once reaching the bottomof the well or perforation P, it can dissolve and permit the heavymaterial to block the perforation P. Still another option is to providecoating with water-activated urethanes which expand, i.e., as waterabsorbs into the urethane polymers.

As generally seen in FIG. 6, it is envisioned that a mud 15 can bepumped via a pump 17 using coiled tubing 13. The mud 15 can includedrilling fluids can be water-based muds (which can be dispersed andnon-dispersed), non-aqueous muds, usually called oil-based mud, andgaseous drilling fluid, in which a wide range of gases can be used orsynthetic mud.

Intersecting the tubing 13 is a chamber 29 which includes a top valve21A and a lower valve 21 B. With valve 21B closed, Valve 21A is open tofill the chamber 29. Then with valve 21A closed, valve 21B can be opento permit the plugging members 16 to mix with the mud 15. The pluggingmembers 16 can preferably be formed in a variety of sizes to permitrestrictions to form and plugging of the well.

Formation F pushes into well at perforations P where production iscoming into well bore B. The plugging members 16 by virtue of theirweight and coating structure are enabled to flow to a point whereby theycan form a restriction in the well, i.e., enable them to fall into thebottom of the well adjacent the perforation P and can aid in blockingthe flow.

In another aspect of the present invention, upon occurrence of ablowout, blowout preventer 14 can be operably disposed over well bore B.In most wells located in bodies of water in the ocean or in waters suchas the Gulf of Mexico, the vertical distance between the water surfaceand the bed S provides ample working room and overhead protection.

Referring to FIG. 2, once so positioned, the blowout preventer 14 isactuated to cause the flow of mud composition 12 which includes pluggingmembers 16 which by virtue of their weight and coating structure areenabled to flow to a point whereby they can form a restriction in thewell. These plugging members 16 migrate through a fluid current to formthe restriction.

When the plug P has terminated or substantially terminated, conventionalmud can then introduced into the tubing string 38 at a pressure which issufficient to overcome the formation pressure and displace the petroleumfluids from the production tubing string 38. The mud 15 flows down holeinto the production string 38 until the weight of the inserted mud issufficient to overcome the formation pressure. Thereafter, the well boreB may be closed and the well may be abandoned or repaired as desired.

It will be appreciated that the method of the present inventionencompasses the steps of inserting plugging materials of the instantinvention into a conduit at a point whereby there is a sufficientopposing current created to permit the free fall of the plugging members16 causing a plug to form internally of the conduit or at the formationzone F. The particular apparatus employed in forming the restriction orin forming the upstream access point for introduction of pluggingmaterials is conventional and improved equipment and techniques foreffecting these steps is anticipated and may form the subject matter offuture patent applications.

It will be understood that other suitable means may be employed forsupplying the plugging members 16 and mud composition 12. If desired,however, other suitable subsurface equipment may be employed for thesame purpose.

The plugging members 16 are denser than the petroleum effluents. It willbe understood, that the method of the present invention is readilycapable of use with plugging members 16 of a suitable density providedwith a coating 19 and or 20 which is preferably non-toxic and able towithstand the rigors of the harsh well environment. The flow ofcomposition 12 must be strong enough to permit the plugging members 16to reach the desired zone or break point.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof and various changes in theprocedures as well as in the details of the described method may be madewithin the scope of the appended claims without departing from thespirit of the invention.

1. A composition for use in plugging a well, which includes a mud havinga plurality of plugging members therein, wherein each said pluggingmember has a density more than about eight times that of water.
 2. Thecomposition of claim 1, wherein said plugging element includes an innercore and an outer cover.
 3. The composition of claim 2, wherein at leastone of said inner core and said outer cover includes a heavy materialhaving a density of more than about eight to twenty times that of water.4. The composition of claim 3, wherein said outer cover includes a dragreducing material.
 5. The composition of claim 3, wherein said outercover includes a dissolvable material.
 6. The composition of claim 3,wherein said plugging member includes an expanding polymer.
 7. A methodfor plugging a well, which includes the steps of: (a) providing acomposition including mud having a plurality of plugging memberstherein, wherein the plugging member has a density more has a densitymore than about eight times that of water; and (b) providing saidcomposition in sufficient opposing fluid flow to fluid flow from anuncontrolled well flow such that said plugging members are enabled todrop by virtue of gravity to a perforation zone where said pluggingmembers impede well flow from said perforation zone.
 8. The method ofclaim 7, wherein step (b) is further characterized to include insertingtubing into said well and delivering said composition through saidtubing.
 9. The method of claim 8, wherein said step (b) is furthercharacterized to provide said tubing in said well to a point adjacent aperforation in said well.
 10. The method of claim 7, wherein said step(a) is further characterized to provide a stream of mud under pressurethrough a conduit and introduce said plugging members into said conduitthrough a valve chamber communicably connected to said conduit.
 11. Themethod of claim 10, wherein said valve chamber is characterized to beinclude a top valve and a lower valve and wherein when said lower valveclosed, top valve is open to fill said chamber with said pluggingmembers, then said top valve is closed and said lower valve is opened topermit said plugging members to mix with said mud.
 12. The method ofclaim 7, wherein step (b) is further characterized to include employinga blow out preventer over said well and delivering said compositionthrough said blow out preventer.
 13. The method of claim 7, wherein saidplugging member includes an inner core and an outer cover.
 14. Themethod of claim 13, wherein at least one of said inner core and saidouter cover includes a heavy material having a density of more thanabout eight times that of water.
 15. The method of claim 14, whereinsaid outer cover includes a drag reducing material.
 16. The method ofclaim 13, wherein said outer cover includes a dissolvable material. 17.The method of claim 13, wherein said plugging member includes anexpanding polymer.
 18. A system for plugging a well, which includes: atank having a mud therein; a conduit connected to said tank; a pumpoperably connected to cause mud to flow through said conduit; a chamberoperably connected to said conduit and including a top valve and a lowervalve and wherein when said lower valve closed, said top valve can beopen to filled said chamber with plugging members, and when said topvalve is closed said lower valve can be opened to permit said pluggingmembers to mix with said mud.
 19. The system of claim 18, wherein saidconduit is operably disposed to terminate adjacent said a perforationzone of the well.